We have two major short-term goals. First, we wish to develop methods that will allow an electron microscopic study of replication in slowly dividing eucaryote cells. Several methods will be used to enrich for replicative growing points, each method will exploit a different characteristic property of these DNA segments. These procedures will allow a direct electron microscopic study of replicating growing points in normal and abnormally growing eucaryote cells. Our second aim is to obtain new information about the process of replication in eucaryotes. Initially we will study the rapidly dividing cleavage nuclei of Drosophila melanogaster (which will not require the above enrichment procedures) and D. melanogaster and HeLa cell lines (which will require enrichment). The short-term goal is to examine the effect of caffeine, ara-A, ara-C, benzo(a)pyrene metabolites and bromouridine onthe replication mechanism. Preliminary experiments with caffeine have shown that this drug relaxes the control of reinitiation in the phage lambda replicator and it is therefore important to determine if it also disturbs similar control systems known to exist in eucaryotes. Our long-term objective is to understand how initiation, directionality and termination are controlled in normal and abnormally growing cells. One important way to obtain this goal is to study how various drugs disturb the replication process. An understanding of these areas is absolutely essential for a firmer grasp of DNA function in normal and abnormal growth, virus infection and mutagenesis.